add cached position for hits

interface/DataLoader.h

@@ -75,6 +75,8 @@ private:
   std::vector<std::vector<SimTrack>> simTracks_;
   std::vector<std::vector<SimVertex>> simVertices_;
 
+  std::unordered_map<uint32_t, std::pair<float, float>> cached_position_;
+
   template <typename T>
   std::vector<std::vector<T>> fillVector(const char *treeName,
                                          const char *branchName, std::shared_ptr<TFile> file, 

src/DataLoader.cc

@@ -179,6 +179,8 @@ void DataLoader::fillHitsSoA() {
       hitsSoA_[i].time[j] = hitsTime[i][j];
       hitsSoA_[i].fraction[j] = 0.f;
       hitsSoA_[i].id[j] = hitsId[i][j];
+
+      cached_position_.emplace(hitsId[i][j], std::make_pair(hitsPos_x[i][j], hitsPos_y[i][j]));
     }
   }
 }